A computer tomograph is an apparatus for producing a three-dimensional image of an object to be examined, in particular of a patient, via x-ray diagnostic methods. A conventional computer tomograph such as is disclosed, for example, in EP 0 296 339 A1 includes a substantially angular supporting frame, denoted as a gantry, having a rotary carriage that can rotate about an isocentric axis, and a support ring, which is stationary with reference to the rotation about the isocentric axis, for bearing the rotary carriage. The rotary carriage and the support ring have a common central opening into which the object to be examined is pushed for imaging. The rotary carriage holds an x-ray emitter for transirradiating the object. The rotary carriage further includes a detector unit that is held on the gantry in a position opposite the x-ray emitter and serves the purpose of recording x-ray projection images of the object.
In the course of a computed tomography examination, such x-ray projection images of the object as the rotary carriage rotates are recorded from a multiplicity of projection directions. Subsequently, a three-dimensional image of the object is calculated in a slicewise fashion via numerical backhand projection methods from the x-ray projection images.
The detector unit of a computer tomograph normally includes a multiplicity of detector elements that are arranged along a detector surface and each have an assigned evaluation electronic. During operation of the computer tomograph, the detector elements and, in particular, their electronic components generate a substantial heat loss that must be dissipated, if only to avoid overheating of the detector unit. Moreover, the maintenance during operation of the computer tomograph of a detector temperature that is as constant as possible is of great importance in order to avoid a so-called temperature drift, that is to say a thermally conditioned change in the recording characteristic of the computer tomograph.
To date, one or more variable-speed fans have frequently been used for cooling such a detector unit, these being directly assigned to the detector and thus being arranged on the rotary carriage. Such a cooling system, in which an oil cooling system is additionally provided, is disclosed, for example, in EP 0 296 339 A1. Because gantry rotational speeds of modern computer tomographs are becoming ever higher with the advancing development, the use of such fans is limited as a consequence of the centrifugal forces occurring and of frequent fan failures thereby caused through bearing damage.
Alternatively, DE 197 04 338 A1 discloses utilizing the airflow caused by the gantry rotation itself to cool electronic power components that are arranged on the rotary carriage of a gantry on a computer tomograph.